Passivation Service

The corrosion behavior of stainless steel is described by the terms “active” and “passive”, with an active steel freely corroding while a passive steel corrodes slightly or not at all. Stainless steel is inherently “passive” and corrosion-resistant because of the invisible, self-healing, self-forming, non-reactive chromium oxide film that is always forming in the presence of oxygen. Often this natural, corrosion resistant barrier is broken down by contaminants during fabrication (usually surface free iron) or deteriorates through oxygen starvation that may occur during shipping or storage. The Passivation of stainless steel refers to a cleaning process in which contaminants, such as surface free iron, are dissolved in a hot nitric acid bath. The nitric acid selectively dissolves surface free iron, and in the process, conditions the steel surface to return to its inherent, self-passivating state.

The decision to use stainless steel is usually based on its intrinsic properties and the benefits of those properties. The term “Stainless” refers to the phenomenon of Passivity, a term which describes the role of Chromium in the steel. In the presence of oxygen, an invisible, non-reactive, chromium oxide film constantly forms on the surface. This self-healing, self-forming property gives stainless steel its shiny appearance yet offers the following benefits:

• Excellent corrosion resistance
• Tough, temperature tolerant mechanical properties
• High level of machinability